1. Field of the Invention
The present invention relates to an above-knee prosthesis and, more particularly to a phase detecting means in a pneumatically or hydraulically controlled teaching playback swing-phase-controlled above-knee prosthesis.
2. Description of the Prior Art
The artificial leg is designed so that a person wearing the artificial leg cannot be easily identified, thus avoiding exerting mental and physical stresses on the person.
FIG. 15 is a diagrammatic illustration showing the sequential variation of the posture of the right half of a normal person, in which indicated at a is the heel, at b is the knee, at c is the hip, at d is the leg, at e is the thigh,. In a stance phase between the landing of the heel a on the floor and the departure of the toe g from the floor, a substantially vertical reaction f of the floor acts on the leg d. A phase between the departure of the toe g from the floor and the next landing of the heel a on the floor is a swing phase.
FIG. 16 shows a conventional above-knee prosthesis incorporating an air cylinder g, disclosed in Japanese Patent Publication No. 52-47638. A thigh frame h and a leg frame i are joined pivotally by a knee shaft j, the extremity of the piston rod of the air cylinder g is joined pivotally to the thigh frame h, and the lower end of the cylinder of the air cylinder g is joined pivotally to the leg frame i. Since the leg frame i swings as a pendulum in a swing phase, a resistance against the flow of air and the expansionary force of compressed air in the air cylinder g serve in substitution for muscles. Thus, the air cylinder g suppresses the upward swing of the heel in the initial stage of a swing phase, allows the subsequent free forward swing of the leg frame i, and brakes the forward swing of the leg frame i in the final stage of the swing phase to mitigate terminal impact. In a stance phase subsequent to the swing phase, the thigh frame h and the leg frame i come into abutment with a stopper k, whereby the knee joint is prevented from drop-off.
FIGS. 17(a), 17(b), 17(c) and 17(d) show another conventional above-knee prosthesis. As shown in FIG. 17(c), a pressure switch consisting of metallic plates m1 and m2 and a compression-conductive rubber plate n placed between the metallic plates m1 and m2 is closed when a pressure exceeding a predetermined level is applied thereto. Then, a microcomputer o (FIG. 17(d)) gives a signal to a driver p to drive a rotary solenoid q so as to control the opening of the valve r of an air cylinder g. In FIGS. 17(a) to 17(d), indicated at s is a power supply.
The motion of the leg frame i relative to the thigh frame h in a swing phase is controlled in a plurality of walking speeds according to a control program organized on the basis of simulated results from a dynamic analysis of various gaits of the normal persons. Therefore, the motion of the leg frame i can be controlled so as to meet different gaits of the normal persons, namely, a gait for normal walking, a gait for rambling and a gait for quick walking, and this above-knee prosthesis is comparatively satisfactory in motion. However, this above-knee prosthesis has the following structural drawbacks to be improved.
(1) The pressure switch requires a large space for installation, which increases the total length of the above-knee prosthesis. Therefore, it is difficult to use the above-knee prosthesis for children and women.
(2) It is highly possible that the pressure switch malfunctions due to variations in the reaction of the ground resulting from variations in the condition of the ground or due to the abrasion of the shafts and sliding parts, which may cause problems in the safety of a person wearing the above-knee prosthesis (hereinafter, referred to as "prosthesis wearer").
(3) The pressure switch is a kind of contact sensor having contact parts which are abraded to reduce the life of the pressure switch.
(4) The above-knee prosthesis requires comparatively troublesome work for adjustment and maintenance.
(5) The exposed wiring of the pressure switch is subject to breakage.
(6) The displacement of the movable parts of the above-knee prosthesis relative to each other for closing and opening the pressure switch is a possible cause of malfunction of the pressure switch and deteriorates walking feeling.
(7) Since the pressure switch and associated parts are provided at a lower position on the leg frame, the sensed weight of the above-knee prosthesis is greater than the actual weight of the same.